How to compare if two structs slices or maps are equal

Question

I want to check if two structs  slices and maps are equal   But I m running into problems with the following code  See my comments at the relevant lines   package main  import        fmt       reflect     type T struct       X int     Y string     Z   int     M map string int    func main         t1    T          X  1          Y   lei           Z    int 1  2  3           M  map string int               a   1               b   2                        t2    T          X  1          Y   lei           Z    int 1  2  3           M  map string int               a   1               b   2                        fmt Println t2    t1        error - invalid operation  t2    t1  struct containing   int cannot be compared       fmt Println reflect ValueOf t2     reflect ValueOf t1         false     fmt Println reflect TypeOf t2     reflect TypeOf t1         true        Update  slice or map     a1      int 1  2  3  4      a2      int 1  2  3  4       fmt Println a1    a2        invalid operation  a1    a2  slice can only be compared to nil       m1    map string int           a   1           b   2            m2    map string int           a   1           b   2            fmt Println m1    m2         m1    m2  map can only be compared to nil      http   play golang org p AZIzW2WunI

User · Answer

reflect DeepEqual is often incorrectly used to compare two like structs  as in your question  cmp Equal is a better tool for comparing structs  To see why reflection is ill-advised  let s look at the documentation   Struct values are deeply equal if their corresponding fields  both exported and unexported  are deeply equal       numbers  bools  strings  and channels - are deeply equal if they are equal using Go s    operator   If we compare two time Time values of the same UTC time  t1    t2 will be false if their metadata timezone is different  go-cmp looks for the Equal   method and uses that to correctly compare times  Example  m1    map string int       quot a quot   1       quot b quot   2    m2    map string int       quot a quot   1       quot b quot   2    fmt Println cmp Equal m1  m2      will result in true

User · Answer

You can use reflect DeepEqual  or you can implement your own function  which performance wise would be better than using reflection    http   play golang org p CPdfsYGNy   m1    map string int          a  1       b  2    m2    map string int          a  1       b  2    fmt Println reflect DeepEqual m1  m2

User · Answer

Here s how you d roll your own function http   play golang org p Qgw7XuLNhb  func compare a  b T  bool     if  amp a     amp b       return true       if a X    b X    a Y    b Y       return false       if len a Z     len b Z     len a M     len b M        return false       for i  v    range a Z       if b Z i     v         return false             for k  v    range a M       if b M k     v         return false             return true

User · Answer

If you re comparing them in unit test  a handy alternative is EqualValues function in testify

User · Answer

Since July 2017 you can use cmp Equal with cmpopts IgnoreFields option   func TestPerson t  testing T        type person struct           ID   int         Name string            p1    person ID  1  Name   john doe       p2    person ID  2  Name   john doe       println cmp Equal p1  p2       println cmp Equal p1  p2  cmpopts IgnoreFields person     ID             Prints         false        true

[go] How to compare if two structs, slices or maps are equal?

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